confused?? or is this correct too?

Paul S_3

I have two photos below,one photo is the manufacturer's booklet from the boiler, send the other photo is of a dirt separator....on almost all of my condensing boiler jobs I always use a air separator and a dirt separator, air separator on supply tied in with the feed and expansion tank......with the circuLation pump pumping away from that point.....and I put the dIrt separator on the return piping..., Why does Rinnai specify the feed, the dIrt separator and the air Eliminator on the return? Thanks Paul s

don_9

bc

Bc they may not know any better.watch out for the new combo unit they no longer have the domestic hot water set point on the control panel.so you can no longer program the water temps to 120.now you have to use a mixing valve to maintain the temps at the facuets.

Tom_133

Internal Pump

I think it's because the internal pump is pushing through the heat exchanger and then out to the supply. If you were to put the air separator on the supply and then tie the expansion tank in there it would knock down the PSI at that point to whatever the expansion tank is set for and you may not have enough psi to circulate properly. It works well to put it on the return. This would only be on the non primary secondary piping.

Ironman

Point Of No Pressure Change

The PONPC is where the internal expansion tank connects to the primary loop inside the boiler. The secondary (house) loop "sees" the entire primary loop as the PONPC. It is the PONPC that the circ should "pump away" from. The air and dirt separators are not the PONPC; the connection point of the expansion tank is.



This can become confusing because we typically connect the xtank to the bottom of the air separator, but it's that connection that's the PONPC, not the air separator itself.



You shouldn't need the external xtank unless the volume of the internal tank is insufficient. In that case, I would recommend that you either connect the extra xtank to the same point as the internal one or disconnect the internal one which would make the house loop the primary. You don't want two PONPCs.



For clarity: it's my understanding that the primary loop is the one where the xtank is connected and has the PONPC there.



Siggy explains it this way in his book too, but some in the industry identify the primary as the boiler loop. This makes it confusing sometimes.

RobG

Just a guess

Just a guess, but I think that with the tight passages on those heat exchangers they want to ensure that no crud gets into the unit. It's probably on the supply to filter any existing debris from an existing cast iron system.



I just pipe them as they recommend. If not piped according to manufactures specs the warranty will not be honored. If you want to deviate from their prints get a new set of prints from them or you will own it!



The Asians are fair but tough to work with. Cross your tee's and dot your I's.



Rob

Paul S_3

Thanks

Thank you guys for ALL your help much appreciated, I'll keep you guys posted Paul S

gennady

Set point

I think it is because code requires mixing valve on all combi units.

gennady

Expansion tank connection.

I think connecting expansion tank to bottom of air separator invites dirt into expansion tank. We stopped doing it and connect tank to the tee on the line before system pump near air separator.